Generic hot rod header question (caps, etc)
 

Was watching one of the Sunday am hot rod shows and they were showing a set of massive headers that could either be run open OR be capped and run through a longer exhaust system including a muffler.

My question is wouldn't running the open headers lean out the mixture if it was normally set for driving with the muffler?

Maybe it's just the large diameter of the collector that is throwing me off but going from that massive tube to a 2" or similar exhaust that then goes through a muffler just seems like two wildly different exhaust scenarios.

In a word, yes.

When I was running at the drag strip with my Camaro, we always ran with the full exhaust while others would run open headers.

They would then wonder why their car ran like crap. Depending on the tune, some engines will respond well to freeing up exhaust but most will run worse.

As the exhaust cools traveling from the engine rearward, one would theoretically need a smaller diameter pipe further back to keep the velocity the same.

I suspect much 'exhaust tuning' is really just loudness enhancement. If it's louder, it feels faster.

Some folks of course run nitrous, which has it's own fuel enrichment circuit along with the funny gas ... that could be set up to run with open headers and the rest of the motor could be set to run with the exhaust system.

Check out Supertraps info... they have, or had some info regarding the length of the exhaust stream... and its effect on power..

what put the quesiton in my head was my recent sport muffler conversion. in reading up on that i found several comments about the mixture leaning out when going from a 1out to a 2 out.

so then i'm thinking if the hot rod carb is tuned with mufflers on for general driving and horseplay then it must lean out when going open pipes presumably at what these ne'r do wells refer to as a speed contest. so they're running the car hardest in a leaned out condition which i thought was bad juju.

seems like without a computer reading the exhaust you only get one or the other.

I happened to revisit Supercraps page when you posted earlier..


http://www.supertrapp.com/technology/index.asp

well it seems i have correctly hypothesized something.

that this something has been known about since the beginning of time is of no consequence to my pride.

neat!